Conventionally, a so-called (½*(L+R)) technique is known in which an L signal and an R signal that are acoustic signals (audio signals) of two channels are used to perform a linear combination on the L signal and the R signal with a scale factor+½. Use of such a technique makes it possible to obtain an acoustic signal of a sound which is localized around the center between a reproduction position where the L signal is reproduced and a reproduction position where the R signal is reproduced (for example, see patent literature (PTL) 1).
Furthermore, a technique is known in which two channel acoustic signals are used to obtain, for each frequency band, a similarity level between audio signals based on an amplitude ratio and a phase difference between the channels, and an acoustic signal is re-synthesized by multiplying a signal of a frequency band having a low similarity level by a small attenuation coefficient. Use of such a technique makes it possible to obtain an acoustic signal of a sound which is localized around the center between a reproduction position where the L signal is reproduced and a reproduction position where the R signal is reproduced (for example, see PTL 2).
With the above-described techniques, an acoustic signal that emphasizes a sound is generated which is localized around the center of the reproduction positions each corresponding to a different one of the two channel acoustic signals.